This study describes the conversion of a 2022 Volkswagen Crafter (VW) 35 TDI340 delivery van from a conventional diesel powertrain into a series–parallel hybrid electric vehicle (HEV). A downsized 1.5 L diesel engine and an electric motor-generator unit are integrated via a planetary power-split device, supported by a high-voltage lithium-ion battery. A MATLAB/Simulink model of the hybrid system is developed, and its speed-tracking PID controller is optimized using genetic algorithms and particle-swarm methods. Simulation results show significant efficiency gains: for example, average fuel consumption falls from 9.952 to 6.913 L/100 km (a 30.5% saving) and CO₂ emissions drop from 260.8 to 181.0 g/km (79.8 g reduction), while vehicle range on a 75 L tank grows by ~43.3% (from 785.7 to 1126.0 km). The optimized series–parallel design greatly improves urban driving economy and reduces emissions without sacrificing performance.